The Darling River (or River Darling; Paakantyi: Baaka or Barka), is the third-longest river in Australia, measuring 1,472 kilometres (915 mi) from its source in northern New South Wales to its confluence with the Murray River at Wentworth. Including its longest contiguous tributaries, it is 2,844 km (1,767 mi) long, making it the longest river system in Australia. The Darling River is the outback's most famous waterway.

As of the early 2020s, the Darling is in poor health, suffering from over-allocation of its waters to irrigation, pollution from pesticide runoff, and prolonged drought. During drought periods in 2019 it barely flowed at all. The river has a high salt content and declining water quality. Increased rainfall in its catchment in 2010 improved its flow, but the health of the river will depend on long-term management.

The Division of Darling, Division of Riverina-Darling, Electoral district of Darling and Electoral district of Lachlan and Lower Darling were named after the river.

Aboriginal peoples have lived along the Darling River for tens of thousands of years. The Barkindji people called it Baaka or Barka, "Barkindji" meaning "people of the Barka".

The Queensland headwaters of the Darling (the area now known as the Darling Downs) were gradually colonized from 1815 onward. In 1828 the explorers Charles Sturt and Hamilton Hume were sent by the Governor of New South Wales, Sir Ralph Darling, to investigate the course of the Macquarie River. He visited the Bogan River and then, early in 1829, the upper Darling, which he named after the Governor. In 1835, Major Thomas Mitchell travelled a 483-kilometre (300 mi) portion of the Darling River. Although his party never reached the junction with the Murray River he correctly assumed the rivers joined.

In 1856, the Blandowski Expedition set off for the junction of the Darling and Murray Rivers to discover and collect fish species for the National Museum. The expedition was a success with 17,400 specimens arriving in Adelaide the next year.

Although its flow is extraordinarily irregular (the river dried up forty-five times between 1885 and 1960), in the later 19th century the Darling became a major transportation route, the pastoralists of western New South Wales using it to send their wool by shallow-draft paddle steamer from busy river ports such as Bourke and Wilcannia to the South Australian railheads at Morgan and Murray Bridge. But over the past century the river's importance as a transportation route has declined.

Large floods occurred in 1974 and 1976.